Use of calcium carbonate in rigid poly(vinyl chloride) compositions

Abstract

Poly(vinyl chloride) is compounded with a chalk-like, essentially pure calcium carbonate to provide improved weathering resistance of rigid poly(vinyl chloride) articles subjected to external exposures of heat and sunlight. Blends and alloys are also disclosed. Optionally, one can add either zinc alkyl ester scavenger, organotin stabilizer, or both to further improve the effectiveness of the essentially pure calcium carbonate.

1. A weather resistant poly(vinyl chloride) compound, comprising:
 (a) poly(vinyl chloride) and 
 (b) at least 2 weight parts of essentially pure calcium carbonate per 100 weight parts of poly(vinyl chloride), the calcium carbonate having a particle size less than 10 μm, wherein the essentially pure calcium carbonate has a purity of at least 95 weight percent and serves as a light stabilizer by scavenging for free hydrochloric acid generated in poly(vinyl chloride) upon exposure to visible and ultraviolet light. 
 
     
     
       2. The compound of  claim 1 , wherein the essentially pure calcium carbonate particle size is less than 6 μm. 
     
     
       3. The compound of  claim 1 , wherein the calcium carbonate is Jamaican calcium carbonate. 
     
     
       4. The compound of  claim 1 , wherein the essentially pure calcium carbonate is present in an amount from about 2 to about 50 weight parts. 
     
     
       5. The compound of  claim 1 , wherein the essentially pure calcium carbonate particles are surface treated with a stearate. 
     
     
       6. The compound of  claim 1 , further comprising:
 (c) at least 0.5 weight parts of organotin heat stabilizer based on 100 weight parts of poly(vinyl chloride), wherein the organotin stabilizer comprises substituted mono-alkyl or dialkyl or trialkyl esters of tin with mono-, di-, or tri-substituted active mercapto groups or carboxylate groups. 
 
     
     
       7. The compound of  claim 6 , further comprising:
 (d) at least 0.1 weight parts of zinc dialkyl ester scavenger per 100 weight parts of PVC resin, provided the equivalents of active mercapto groups or carboxylate groups in the organotin are equal to or exceed the equivalents of dialkyl ester groups in the zinc dialkyl ester. 
 
     
     
       8. The compound of  claim 1 , wherein the poly(vinyl chloride) comprises is a homopolymer or a copolymer of copolymerized vinyl chloride monomer with less than 5% by weight copolymerized other unsaturated co-monomer. 
     
     
       9. A compound comprising a mixture of polymers, wherein one polymer is the compound of  claim 1  and wherein a second polymer is a poly(acrylic) polymer. 
     
     
       10. The compound of  claim 9 , wherein the poly(acrylic) polymer is a poly(meth)acrylate present in the mixture in an amount from about 25 to about 75 weight percent of the mixture. 
     
     
       11. A process for producing a poly(vinyl chloride) compound, the process comprising:
 (a) providing an essentially pure calcium carbonate having a particle size less than 10 μm; and 
 (b) mixing the calcium carbonate with poly(vinyl chloride) in an amount of at least 2 weight parts calcium carbonate per 100 weight parts of poly(vinyl chloride), wherein the essentially pure calcium carbonate has a purity of at least 95 weight percent and serves as a light stabilizer by scavenger for free hydrochloric acid generated in poly(vinyl chloride) upon exposure to visible and ultraviolet light. 
 
     
     
       12. A poly(vinyl chloride) article comprising the compound of  claim 1 . 
     
     
       13. The article of  claim 12 , wherein the essentially pure calcium carbonate particle size is less than 6 μm. 
     
     
       14. The article of  claim 12 , wherein the calcium carbonate is Jamaican calcium carbonate. 
     
     
       15. The article of  claim 12 , wherein the essentially pure calcium carbonate is present in an amount from about 2 to about 50 weight parts and is surface treated with a stearate. 
     
     
       16. The article of  claim 12 , wherein the compound further comprises:
 (c) at least 0.5 weight parts of organotin heat stabilizer based on 100 weight parts of poly(vinyl chloride), wherein the organotin stabilizer comprises substituted mono-alkyl or dialkyl or trialkyl esters of tin with mono-, di-, or tri-substituted active mercapto groups or carboxylate groups. 
 
     
     
       17. The article of  claim 16 , wherein the compound further comprises:
 (d) at least 0.1 weight parts of zinc dialkyl ester scavenger per 100 weight parts of PVC resin, provided the equivalents of active mercapto groups or carboxylate groups in the organotin are equal to or exceed the equivalents of dialkyl ester groups in the zinc dialkyl ester. 
 
     
     
       18. The article of  claim 12 , wherein the poly(vinyl chloride) comprises is a homopolymer or a copolymer of copolymerized vinyl chloride monomer with less than 5% by weight copolymerized other unsaturated co-monomer. 
     
     
       19. The article of  claim 12 , where the compound comprises a mixture of polymers, wherein one polymer is the compound of  claim 1  and wherein a second polymer is a poly(acrylic) polymer. 
     
     
       20. The article of  claim 12 , wherein the compound comprises a mixture of polymers, wherein one polymer is the compound of  claim 7  and wherein a second polymer is a poly(acrylic) polymer.